Absorption refrigeration



J1me 1957 A. G. HELLSTROM 2,795,941

ABSORPTION REFRIGERATION Original Filed May 15, 1953 lllllllllllllllll IN! E NTOR.

A44 zrromvsr United States Patent ABSORPTION REFRIGERATION Axel GostaHellstrom, Johanneshov, Sweden, assignor to Aktiebolaget Elektrolux,Stockholm, Sweden, 1! corporation of Sweden Continuation of applicationSerial No. 355,329, May 15, 1953. This application May 29, 1956, SerialNo. 588,126

Claims priority, application Sweden May 16, 1952 18 Claims. (Cl.62-119.5)

My invention relates to absorption refrigeration, and more particularlyto such a refrigeration system employing an auxiliary pressureequalizing gas. This application is a continuation of my applicationSerial No. 355,329, filed May 15, 1953, now abandoned.

It has been proposed in refrigeration systems of this kind to adjust theconcentration of refrigerant in the absorption liquid circuit byaccumulating liquid refrigerant with variations in operating conditions,and subsequently redistributing absorption liquid in the absorptionliquid circuit to cause such accumulated refrigerant to be introduced ina positive and controlled manner into the absorption liquid circuit.Such redistribution of absorption liquid in its circuit may be effectedby making use of absorption liquid available in certain parts of theabsorption liquid circuit when normal circulation of absorption liquidis terminated or substantially reduced.

in order to introduce the accumulated liquid refrigerant in an effectivemanner into the absorption liquid circuit, it is extremely important foran adequate quantity of absorption liquid to be redistributed ortransferred in such circuit. In many instances the quantity ofabsorption liquid available for redistribution or transfer in theabsorption liquid circuit is below a definite critical value andinadequate to effect complete mixing of accumulated liquid refrigerantwith absorption liquid when it is desired to return the refrigerant tothe absorption liquid circuit. This is objectionable because the fulladvantages for effecting return of accumulated refrigerant to theabsorption liquid circuit by redistribution of absorption liquid are notrealized.

The object of my invention is to provide an improvement for adjustingmore precisely the concentration of refrigerant in the absorption liquidcircuit. I accomplish this by storing a quantity of absorption liquid inthe absorption liquid circuit in such a manner that such stored liquidis withheld or withdrawn from circulation during normal operation of thesystem and promptly made avail able, when redistribution of theabsorption liquid occurs, to insure nice control of the introduction ofaccumulated liquid refrigerant into the absorption liquid circuit.

The above and other objects and advantages of the invention will becomeapparent as the following description proceeds, and the features ofnovelty which characterize my invention will be pointed out withparticularity in the claims annexed to and forming a part of thisspecification.

For a better understanding of my invention, reference may be had to thefollowing description taken in connection with the accompanying drawingin which:

Fig. 1 illustrates more or less diagrammatically an absorptionrefrigeration system of the inert gas type embodying the invention; and

Fig. 2 is a fragmentary view of a refrigeration system like that shownin Fig. l diagrammatically illustrating another manner of heating thesystem.

Referring to Fig. 1, l have shown my invention in connection with anair-cooled absorption refrigeration system of a uniform pressure type inwhich an auxiliary pressure equalizing gas is employed. Systems of thistype are well known and include a cooling unit or evaporator structure10 which is arranged to abstract heat from the thermally insulatedinterior of a refrigerator cabinet. Refrigerant fluid, such as ammonia,flows through a conduit ll into the cooling unit 10 and evaporates anddiffuses therein into an inert gas, such as hydrogen, to produce arefrigerating effect. The resulting gas mixture of refrigerant and inertgas flows from cooling unit 10 through a conduit 12, gas heat exchanger14 and vertically extending conduit 15 into an air-cooled absorber unit16 comprising a shell or container 17 and a looped coil 18.

In the absorber unit 16 refrigerant vapor is absorbed by a suitableabsorbent, such as water, for example, which is introduced into coil 18through a conduit 19. The hydrogen or inert gas, which is practicallyinsoluble and weak in refrigerant, is returned through gas heatexchanger 14 to the lower end of cooling unit 10. During operation ofthe refrigeration system, heat is liberated in the absorber unit 16 dueto absorption of refrigerant vapor into absorption liquid. Such heat ofabsorption is given up to surrounding cool air which passes over thesurfaces of the absorber unit and the temperature of which is determinedby the temperature of the cool air flowing in heat exchange relationtherewith.

The circulation of gas in the gas circuit just described is due to thedifference in specific weight of the columns of gas rich and weak,respectively, in refrigerant vapor. Since the column of gas rich inrefrigerant vapor and flowing from the upper end of cooling unit 10 tothe absorber coil 18 is heavier than the gas weak in refrigerant vaporand flowing from such coil to the lower end of the cooling unit, a forceis produced or developed within the system for causing circulation ofinert gas in the manner described.

From the container 17 enriched absorption liquid, which is also referredto as absorption solution, is conducted through a conduit 20 and liquidheat exchanger 21 into a vapor lift pump 22 of a generator or vaporexpulsion unit 23. The generator 23 comprises a heating tube 24 havingthe vapor lift pump 22 and a boiler 25 in thermal exchange relationtherewith. By heating generator 23, as by fluid fuel burner 26, forexample, liquid from the heat exchanger 21 is raised by vapor liftaction through pump 22 into the upper part of boiler pipe 25. Theliberated refrigerant vapor entering boiler pipe 25 through the pump 22,and also vapor expelled from solution in the boiler pipe, fiows upwardlyinto an air-cooled condenser 27 in the form of a coil having fins fixedthereto.

Refrigerant vapor is liquefied in the condenser 27 by surroundingcooling air which flows over the surfaces of the coil and fins, and theliquefied refrigerant is returned to the cooling unit 10 through theconduit 11 to complete the refrigerating cycle. Liquid refrigerant flowsby gravity in the cooling unit 10 in the presence of upwardly flowinginert gas, the inert gas flowing upwardly in counterflo'w to therefrigerant in a low temperature section 10a and then in a highertemperature section 1%. The lower end of condenser 27 is connected by aconduit 28 to the gas circuit, as to the gas heat exchanger 14, forexample, so that any non-condensable gas that may pass into thecondenser will flow to the gas circuit and not be trapped in thecondenser. The weakened absorption solution, from which refrigerant hasbeen expelled, is conducted from boiler pipe 25 through a conduit 29,liquid heat exchanger 21 and conduit 19 into the upper part of absorbercoil 18. Circulation of absorption solution in the manner just describedis due to raising of liquid from a low level to a higher level I inboiler pipe 25. Absorption liquid flows downwardly from level I ingenerator 23 and overflows from the upper end of conduit 19 into theupper end of the absorber coil 18 at the level II. The quantity ofliquid held in boiler pipe between the levels I and II defines thestatic pressure head required to overcome the resistance offered to flowof liquid from the boiler pipe to the upper end of the absorber coil 18.

The refrigeration system just described may be controlled by a thermalbulb which is affected by a temperature condition of cooling unit 10. Asshown, the thermal bulb 30 is arranged in thermal exchange relation withthe bottom part of low temperature section 100 of cooling unit 10 andconnected by a conduit 31 to a control device 32 which is connected in afuel supply conduit 33 of burner 26. The thermal bulb 30 and conduit 31may form part of an expansible fluid thermostat which is charged with asuitable volatile fluid and responds to changes in temperature ofcooling unit 10 to operate control device 32, in a manner well known inthe art.

When the temperature of cooling unit 10 increases due, for instance, toincrease in heat load caused by placing of warm material in thethermally insulated interior of the refrigerator, or rise in room airtemperature, the thermal bulb 30 in normal operation of therefrigeration system becomes effective to operate control device 32 toincrease the supply of fuel to burner 26. This increases the heat inputand hence the rate at which refrigerant vapor is expelled from solutionin generator 23, thereby increasing the amount of refrigerant vaporwhich condenses in condenser 27 and flows into cooling unit 10.Conversely, when the temperature of cooling unit 10 decreases, thethermal bulb 30 becomes effective to operate control device 32 todecrease the supply of fuel to burner 26. This reduces the heat inputand hence the rate at which refrigerant vapor is expelled from solutionin generator 23, thereby decreasing the amount of refrigerant vaporwhich condenses in condenser 27 and flows into cooling unit 10.

The thermostatic control just described is of the kind in which thesupply of fuel desirably is reduced to such an extent that substantiallyno vapor is expelled from solution in generator 23 when the cooling unit10 reaches a predetermined low temperature. In other words, under theseconditions only a sufficient quantity of fuel is supplied to the burner26 to maintain the latter ignited and only heat of liquid is supplied tothe solution in generator 23 at such times. When the fuel supply toburner 26 is inadequate for the burner to supply heat of vaporization tothe solution in the generator, no expulsion of refrigerant vapor fromsolution will take place and the solution will be maintained below itsboiling temperature. Since no expulsion of vapor from solution will takeplace in generator 23 when the supply of fuel to burner 26 is reducedsufliciently by the thermostatic control in the manner just explained,no lifting of liquid by vapor lift action Will take place in the vaporlift pump 22 under these conditions and the circulation of absorptionsolution through and between the generator 23 and absorber unit 16 willstop. Hence. when the thermostatic control provided acts to reduce thesupply of fuel to burner 26 and refrigerant vapor is no longer expelledfrom solution in the generator 23 and pump 22 is no longer effective toraise liquid to cause circulation of absorption solution, the supply ofheat to the generator 23 for the purpose of producing usefulrefrigeration is interrupted and essentially cut off for all practicalpurposes.

In Fig. 2 is illustrated another manner of supplying heat to thegenerator 23 by an electrical heating element 34 disposed within thelower part of heating tube 24. In this instance the control device 32forming part of the expansible fluid thermostat is operativelyassociated with a switch 35 connected in one of the conductors 36 forsupplying electrical energy to heating element 34. The controlarrangement of Fig. 2 is of the on" and off type in which the thermalbulb 30 becomes effective to cause control device 32 to close switch 35and energize heating element 34 when the temperature of cooling unit 10increases due to increase in load. Conversely, when the cooling unit 10reaches a predetermined low temperature the thermal bulb 30 becomeseffective to cause control device 32 to open switch 35 and disconnectheating element 34 from the source of supply of electrical energy. InFig. 2 switches 37 and 38 are associated with the thermostaticallycontrolled switch 35 for controlling the supply of electrical energy tothe heating element 34.

The refrigeration system of Fig. l embodies provisions for adjusting theconcentration of refrigerant in the absorption liquid circuit byaccumulating and storing liquid refrigerant with variations in operatingconditions, and subsequently introducing such stored liquid refrigerantinto the absorption liquid circuit in a controlled manner. In Fig. 1this is accomplished by providing in the container 17 a baffle orpartition 39 to form adjacent spaces or vessels 40 and 41. The vessel 40functions as the absorber vessel having a liquid inlet at the upper endthereof which receives absorption liquid from the lower end of theabsorber coil 18 and in which space is maintained a body of absorptionliquid enriched in refrigerant. The absorber vessel 40, through whichflow of liquid is effected from coil 18 to conduit 20 connected thereto,forms an active portion of the absorption liquid circuit in which theliquid normally circulates during operation of the refrigeration system.

The vessel 41 functions as an accumulation or concentration vessel inwhich is stored unevaporated refrigerant passing from the cooling unitor evaporator 10. Such excess or unevaporated refrigerant passes fromthe lower end of cooling unit 10 and flows along the bottom part of thegas heat exchanger 14 and conduit 15 into the vessel 41, theunevaporated refrigerant entering the vessel 41 through conduit 15 withinert gas enriched in refrigerant. A conduit 42 connects the bottom partof vessel 41 and an upper part of the conduit 20 at the vicinity ofvessel 40. In this way a region below the liquid surface level of theliquid body in vessel 41 is in free liquid communication with a regionbelow the liquid surface level of the liquid body in vessel 40, theconnecting passage provided by the conduit 42 being completely filledwith liquid under all operating conditions of the system. Free liquidcommunication is established in such a manner between the liquid bodiesin vessels 40 and 41 that vessel 41 constitutes a part which is disposedoutside the active portion of the absorption liquid circuit and in whichnormal flow of absorption liquid is absent.

In view of the foregoing, it will now be understood that a body ofabsorption liquid is held in the absorber vessel 40 and that absorptionliquid passes through conduit 42 into the vessel 41. Under certainoperating conditions unevaporated refrigerant also passes from thecooling unit 10 into the vessel 41 and accumulates therein. The inertgas enriched in refrigerant and flowing from the cooling unit 10 throughthe conduit 15 passes through the vapor space of vessel 41 and thenenters the vapor space of absorber vessel 40 through an opening 43 inthe upper part of partition 39. From vessel 40 inert gas enriched inrefrigerant flows upwardly through coil 18 in counterflow to theabsorption liquid flowing downwardly therein.

As long as the liquid surface level in accumulation vessel 41 remainsbelow the opening 43 in partition 39, the unevaporated liquidrefrigerant accumulated therein essentially will be withdrawn from theabsorption liquid circuit. Such refrigerant will be absorbed intoabsorption liquid held in vessel 41 and increase the concentration ofrefrigerant in such absorption liquid to a value materially greater thanthe concentration of refrigerant in the absorption liquid in vessel 40which flows therefrom through conduit 20. By reason of the free liquidcommunication provided by conduit 42 between the liquid body in vessel41 and the active portion of the absorption liquid circuit, sometransfer of accumulated refrig erant by diffusion from vessel 41 intothe active portion of the absorption liquid circuit cannot be avoided.Such transfer of accumulated refrigerant, which involves equalization ofthe concentration of refrigerant in the liquid body in vessel 41 andliquid in the active portion of the absorption liquid circuit, takesplace relatively slowly and without the exercise of any positivecontrol.

However, in Fig. 1 stored liquid refrigerant in vessel 41 is positivelyintroduced into the active portion of the absorption liquid circuit in acontrolled manner by redistributing the absorption liquid in its circuitand increasing the quantity of such liquid held in the vessel 40. Thequantity of liquid held in vessel 40 is increased when the heat supplyto the generator 23 is reduced sufficiently to render the vapor liftpump 22 inactive, thereby terminating the raising of absorption liquidto the level I in Fig. 1. Under these conditions normal circulation ofliquid stops and the quantity of liquid held in boiler pipe 25 betweenthe levels I and II spills over into the upper end of the absorber coil18 from conduit 19. When the pump 23 becomes inactive, some liquid is,therefore, transferred from boiler 25 to absorber coil 18 and eventuallycollects in the vessel 40. Also, liquid contained in the absorber coil18 and wetting the inner wall surfaces thereof will flow downwardytherefrom into the absorber vessel 40 to increase the quantity ofabsorption liquid held in vessel 40 and raise the liquid surface leveltherein.

When ammonia and water are employed as the refrigerant and absorptionliquid, respectively, and unevaporated ammonia passes from the coolingunit and accumulate in vessel 41 and forms a part of the liquid bodytherein, the liquid surface level in vessel 41 will be higher than thatin vessel 40 depending upon the increase in concentration of ammonia inthe absorption liquid in ves sel 41. This is so because, as unevaporatedammonia collects in vessel 41, the specific gravity of the absorptionliquid in that vessel decreases and a liquid body of greater height isrequired in vessel 41 to balance the body of absorption liquid of lessheight in vessel 40. Such higher liquid level in the vessel 41 may berepresented by the dotted line A in Fig. 1 while the lower liquid levelin the vessel 40 may be represented by the dotted line B. Whenunevaporated ammonia has accumulated in vessel 41 and absorption liquidheld in other parts of the system is transferred to the absorber vessel40, the quantity of liquid in the latter increases and the liquidsurface level therein rises.

When the liquid surface level in vessel 40 increases, a similar increasein liquid surface level also takes place in vessel 41. Since the liquidsurface in vessel 41 is at a higher level than in vessel 40 when liquidrefrigerant has accumulated in the former, as just explained, and theliquid surface levels in both vessels increase when an adequate quantityof absorption liquid is transferred to vessel 40, it will be evidentthat liquid in vessel 41 will be the first to reach the level C of theopening 43 and overflow therethrough into vessel 40. In this way liquidrefrigerant accumulated and stored in vessel 41 can be positivelytransferred therefrom into vessel 40 which, as previously explained,forms a part of the active portion of the absorption liquid circuit.Further, liquid refrigerant is transferred from vessel 41 to vessel 40responsive to increase in the surface level of liquid in the vessel 40,such transfer of liquid being effected at a rate faster than that atwhich liquid refrigerant can be transferred by diffusion from vessel 41through conduit 42 to the active portion of the absorption liquidcircuit.

Let us assume that an air-cooled refrigeration system generally likethat shown in Fig. l and described above is charged with ammonia,hydrogen and water so that the system will operate in a satisfactorymanner in a normal temperature range of about 70 F. When the circulationpump 22 in the absorption liquid circuit is operating, an equilibriumcondition is established in which absorption liquid flows at a certainrate into vessel 40 and is with drawn therefrom to the generator 23 atessentially the same rate and the liquid surface levels in the vessels40 and 41 are practically constant. Under these conditions the liquidcolumn in vessel 40 and upper part of conduit 20 balances the liquidcolumn in vessel 41 and conduit 42, the gas pressures acting on theliquid surfaces of the liquid bodies in vessels 40 and 41 being thesame.

Active circulation of absorption liquid only takes place through vessel40 during normal operation and the conduit 42 and vessel 41 essentiallyconstitute a dead-end appendage for absorption liquid in which theliquid body is more or less stagnant. In such normal operation of thesystem the thermostatic control will be operable to shut off the heatsupply to the generator 23 when the cooling unit 10 reaches apredetermined low temperature and substantially all of the liquidrefrigerant will be evaporated therein and possibly also in the gas heatexchanger 14. Also, the absorber vessel 40 will function in the normalmanner explained above the concentration of refrigerant in the liquidheld in the vessels 40 and 41 will be approximately the same. When thereis a slight change in the liquid level in vessel 41 during normaloperation of the system there is a corresponding change in the liquidlevel in vessel 40, because the liquid columns of these liquid bodiesbalance one another.

Let us now assume that the ambient air temperature increases to about F.so that the heat of absorption produced in the absorber unit 16 underthe new operating conditions is not effectively given up to the ambientair flowing in thermal relation therewith. Under such conditionsrefrigerant vapor is not effectively absorbed into absorption liquid inthe absorber unit 16, and inert gas will flow to cooling unit 10 havingan abnormally high concentration of refrigerant vapor so that thecooling unit 10 will not be capable of producing the desired lowrefrigerating temperature for which the thermostatic control isadjusted. Under these assumed conditions. the thermostatic control willfunction to continue the heat supply to the generator 23. By reason ofthe abnormally high partial pressure of refrigerant vapor in the inertgas introduced into the cooling unit 10, all of the liquid refrigerantsupplied to the cooling unit will not be evaporated therein and theexcess unevaporated refrigerant passing from the cooling unit 10 willflow to the vessel 41 in which it is accumulated and stored. By storingunevaporated liquid refrigerant in vessel 41, such refrigerant in effectis withheld or withdrawn from the absorption liquid circuit; and theconcentration of refrigerant in the absorption liquid eventually will bereduced adequately so that absorption liquid having a sufficiently lowconcentration of refrigerant will be supplied to absorber unit 16 fromgenerator 23. This will enable the absorber to function properly even atthe higher ambient air temperature, thereby enabling the absorber tosupply inert gas to cooling unit 10 which is sufficiently poor inrefrigerant vapor to cause substantially all of the liquid refrigerantto evaporate in the cooling unit 10 and gas heat exchanger 14.

When the ambient air temperature decreases from the high value assumedabove and begins to approach the normal temperature range, it is highlydesirable to increase the concentration of refrigerant in the absorptionliquid as soon as possible. This is so because, in the lower or normaltemperature range, such increase in concentration of refrigerant in theabsorption liquid makes it possible to operate the generator 23 at alower temperature which means that the radiation losses will be reduced.the generator can be operated with less heat input, and therectification losses will be decreased.

Such decrease in ambient air temperature to the normal temperature rangemay occur during the night time, for example, which in turn reduces theload on the refrigeration system. Under these conditions the temperatureof cooling unit 10 also will decrease; and, when the latter reaches thepredetermined low temperature referred to above, the thermostaticcontrol will be operable to shut off the heat supply to the generator23. As explained above, this will interrupt the normal circulation ofabsorption liquid and because such liquid to be transferred to thevessel 40 from other parts of the system. By reason of the free liquidcommunication between the vessels 40 and 41 which is always completelyfilled with liquid, absorption liquid flows from vessel 40 through theupper part of conduit 20 and conduit 42 into vessel 41 when absorptionliquid is transferred to vessel 40. When an adequate quantity ofabsorption liquid is transferred to the vessel 40 from other parts ofthe system. liquid refrigerant will be transferred from vessel 41 tovessel 40 through the opening 43 in partition 39 responsive to illcreasein liquid level in the vessel 40. The liquid remaining in accumulationvessel 41 will be diluted to some extent by the absorption liquid whichpasses therein from the absorber vessel 40 through conduits 20 and 42.Accordingly, the absorption liquid passing into vessel 41 through thefiuid communication passage from the vessel 40 will reduce theconcentration of refrigerant in the liquid in vessel 40 and there willbe a tendency for the refrigerant concentration to equalize in theliquid bodies in vessels 4t) and 41.

After an interval of time, the temperature of evaporator 10 will risesufficiently to cause the thermostatic control to function and start theheat supply to the generator 23 at which time pump 22 becomes active.Liquid will now be withdrawn from vessel 40 since it forms a part of theactive portion of the absorption liquid circuit. At the same time someliquid will also be withdrawn from vessel 41 by the pump 22, although itshould be understood that normal circulation of absorption liquid inthis vessel usually is absent. After the pump 22 starts raising liquidinto the upper end of the boiler pipe 25, an interval of time will passbefore absorption liquid again flows into vessel 40. Hence, the entirequantity of liquid held in the container 17 will be reduced to an extentcorresponding to the accumulation of liquid in the container 17 when thenormal circulation of absorption liquid is reduced and liquid istransferred to absorber vessel 40. When the new pumping periodcommences, the part of boiler pipe 25 between the levels I and II isdepleted of liquid; and the absorber coil 18 can accumulate acomparatively large amount of liquid at the inner wall surfaces thereof,due to the action of capillary and adhesive forces, before a stream ofliquid passes through the entire length of the absorber coil. In view ofthe manner in which normal circulation of absorption liquid is resumed,a certain amount of absorption liquid relatively rich in refrigerantwill pass from vessel 41 into the active portion of the absorptionliquid circuit when ing a shut down period.

When absorption liquid again enters vessel 40 from coil 18 and anequilibrium condition is established, the liquid levels in vessels 40and 41 will be essentially the same due to the free liquid communicationtherebetween and the same gaseous atmosphere enveloping the liquidbodies in both vessels. When excess liquid refrigerant enters vessel 41through conduit 15, the liquid surface level in vessel 41 will rise.Under such conditions, the only flow of liquid from vessel 41 to theabsorption liquid circuit will be that quantity necessary to maintain abalancing liquid head in the vessel 40.

In addition to having a free liquid communication be tween the liquidbodies in vessels 40 and 41 beneath the liquid surface levels thereof,it is extremely important in the operation of a system like that shownin Fig. l and just described for an adequate quantity of absorptionliquid to be transferred from other parts of the system to the absorbervessel 40 when the supply of heat to genera tor 23 is reduced and thepump 22 is rendered inactive. When the quantity of absorption liquidtransferred to the absorber vessel 40 is less than a definite criticalvalue, the quantity of absorption liquid passing from the vessel 40through the upper part of conduit and conduit 42 to the accumulation orconcentration vessel 41 will be inpumping is started follow- 8 adequateto effect complete mixing of absorption liquid with liquid refrigerantin the vessel 41.

When the mixing of liquid refrigerant with absorption liquid, such asammonia with water, for example, is in complete in vessel 41, the fulladvantages of the accumulation vessel 41 are not realized. This is sobecause a certain amount of such mixture of refrigerant and absorptionliquid, a mixture which is relatively rich in refrigerant when completemixing is effected, will pass from vessel 41 into the active portion ofthe absorption liquid circuit when operation of the refrigeration systemis again initiated and pumping is resumed following a shut down period.When the quantity of liquid refrigerant transferred from vessel 41 tovessel 40 through the opening 43 in partition 39 is reduced andsubstantially negligible, because the liquid surface level in vessel 41does not rise above the level C when absorption liquid is transferred tothe vessel 40 from other parts of the system, the liquid refrigerantmixed with the absorption liquid in the vessels 40 and 41 and initiallywithdrawn therefrom when operation of the pump 22 is instigated,especially the enriched liquid in the accumulation vessel 41,constitutes the bulk of the refrigerant returned to the active portionof the absorption liquid circuit. Hence, it is extremely desirable totransfer an adequate quantity of absorption liquid to the vessel 40 fromother parts of the system when redistribution of such liquid isefi'ected, so that complete mixing of absorption liquid will be effectedwith the liquid refrigerant accumulated in the vessel 41. In this wayoptimum benefits of the accumulation vessel 41 are gained even when theliquid surface does not rise above the level C when redistribution ofabsorption liquid takes place.

in accordance with my invention, in order to insure the transfer of anadequate quantity of absorption liquid to the vessel 40 in Fig. 1 whenthe pump 22 is rendered inactive, a storage vessel 44 is connected inthe active portion of the absorption liquid circuit between the absorbercoil 18 and absorber vessel 40, the storage vessel 44 serving to arrestflow of absorption liquid in its circuit and enabling a body of arrestedliquid to be retained therein. When normal circulation of absorptionliquid in its circuit is established, the liquid passes from the extremelower end of the coil 18 into the storage vessel 44 from which liquidfiows through a vertically extending conduit 45 into the upper end ofthe absorber vessel 40. The upper end of conduit 45 is at a level Dwhich coincides with and is substantially at the same level as theextreme lower end of the coil 18. During normal operation of the systema body of absorption liquid is held in the storage vessel 44 having aliquid surface at the level D, and absorption liquid discharging fromthe lower end of the coil 18 simply overflows into the upper end of theconduit 45 and passes into the absorber vessel 40. During normaloperation when equilibrium conditions in the system are attained,absorption liquid is supplied in this way to the absorber vessel 40 at arate which is sub stantially the same as that at which absorption liquidis withdrawn from vessel 40 by the pump 22.

When the heat supply to the generator 23 is stopped or reduced, by thethermostatic control shown in Figs. 1 and 2, to render pump 22 entirelyor practically inactive, an adequate quantity of absorption liquid inthe absorber vessel 40 is insured by transferring thereto the body ofabsorption liquid held in the storage vessel 44 as well as from otherparts of the system in the manner explained above. Such transfer ofliquid from storage vessel 44 may be effected by a suitable wick 46provided about conduit 45 for drawing liquid upwardly by capillaryaction at the outer surface of such conduit. The wick 46 may be formedof metal screening having one portion extending downwardly at the outersurface of the conduit 45 and another portion which extends downwardlyinto the interior of the conduit. The wick 46 desirably must be sodimensioned that it draws liquid at a rate which is less than the rateat which absorption liquid flows into the vessel 44 from the absorbercoil 18 during normal operation of the refrigeration system whencirculation of absorption liquid is being effected by the pump 22. Suchdimensioning of the wick 46 is necessary in order that a body ofabsorption liquid will collect in the storage vessel 44 to the level Dduring normal operation of the system.

It has been explained above that absorption refrigeration systems of thekind under consideration may be operated more economically and with lesspower consump tion when provision is made for varying the concentra tionof refrigerant in the absorption liquid for the different operatingconditions encountered. This is especially true when the accumulationvessel 41 makes it possible to operate such a system with absorptionsolution having a relatively high concentration of refrigerant whileunder thermostatic control. However, the power consumption becomesimpaired when the refrigerant concentration in the absorption solutionexceeds a definite high value. This is due to decrease in absorberefficiency with increase in refrigerant concentration of the absorptionsolution which in turn causes the cooling unit or evaporator to operateat a higher temperature. Under these conditions the refrigeration systemmust operate for a longer interval of time to produce a definite lowtemperature in the interior of a refrigerator cabinet, thereby producinga situation where there is a greater likelihood of unevaporatcdrefrigerant passing from the cooling unit without produc ing usefulrefrigeration.

In accordance with this invention, in order to prevent loss ofunevaporated refrigerant from the cooling unit during an on or heatingperiod and to utilize such refrigerant to produce useful refrigerationduring the succeeding off period when the heat supply is terminated, thelow temperature section a of the cooling unit it) is formed of piping ortubing having a cross-sectional area greater than that of the highertemperature section 1% and a dam or overflow point 47 is provided at theend of such low temperature section at the region weak inert gas flowsinto the presence of liquid refrigerant retained therein. For arefrigeration system of a given capacity, the low temperature section1.0a of the cooling unit can be correctly dimensioned so that all of theliquid refrigerant retained therein will evaporate and such lowtemperature section will be depleted of liquid during the off period;and liquid refrigerant will reach the liquid outlet end of the lowtemperature section 10a during the succeeding on or heating periodbefore the thermostat operates to terminate such heating period. Byproviding the dam 47 and preventing flow of unevaporated refrigerantfrom the cooling unit 10 for the particular operating conditionsreferred to above, it will be evident that a refrigeration system may beoperated more ciliciently than would otherwise be possible. However, therefrigerant accumulating vessel 41 does function to improve theoperation of absorption refrigeration systems under the differentoperating conditions encountered, as explained above.

It has been pointed out above that absorber coil 18 can accumulateliquid at the inner wall surface thereof before a stream of liquidpasses through the entire length of the coil. Such liquid is accumulatedat the inner wall surface of the coil due to the action of capillary andadhesive forces and results from absorption liquid being circulatedthrough the absorber coil. However, the liquid accumulating in theabsorber coil and wetting the inner surface thereof is not arrested andretained in a particular place in the same sense that flow of liquid isarrested by the storage vessel 44 when liquid enters the latter.

It has also been pointed out above that the quantity of liquid held inboiler pipe between the levels I and II defines the static pressure headrequired to overcome the resistance offered to flow of liquid from theboiler pipe to the upper end of the absorber coil 18. However, theliquid held in the upper portion of the boiler pipe 25, between theliquid levels I and II, is not arrested and retained in a particularplace in the same sense that fiow of liquid is arrested by the storagevessel 44 when liquid enters the latter.

Accordingly, the expressions arresting absorption liquid, retaining sucharrested liquid and structure for arresting and retaining absorptionliquid, which are employed in the claims, are intended to cover anarrangement like that exemplified in the preferred embodimentillustrated and described above in which a storage vessel 44 or similarstructure is provided to arrest" flow of absorption liquid beingcirculated and to retain" the arrested liquid rather than to a type ofliquid accumulation that takes place when the inner surface of theabsorber coil 18 becomes wetted as the result of absorption liquidflowing therethrough, and to a type of liquid accumulation in the upperpart of the boiler pipe 25 which provides the necessary static head toovercome friction losses in the path of flow of absorption liquid to theupper part of the absorber coil 18. Further, it is desired to point outthat subject matter common to the instant application and to Kogelapplication Serial No. 355,289, filed May 15, 1953, and not beingclaimed herein, is being claimed in the aforementioned Kogelapplication.

Although a single embodiment of the invention has been shown anddescribed, it will be apparent to those skilled in the art that variousmodifications and changes may be made without departing from the spiritand scope of the invention. It is therefore contemplated to cover allmodifications and changes which come within the true spirt of theinvention, as pointed out in the following claims.

What is claimed is:

1. In the art of refrigeration with the aid of a system in whichrefrigerant vapor is expelled from absorption liquid in a generator,refrigerant vapor is liquefied, liquid refrigerant evaporates in thepresence of an inert gas in an evaporator, refrigerant vapor is absorbedinto absorption liquid in an absorber, inert gas is circulated betweenthe evaporator and absorber and absorption liquid is circulated in apath of flow through and between the generator and absorber, theimprovement which comprises the steps of maintaining a body ofabsorption liquid in a first place in contact with inert gas and also inthe path of fiow of absorption liquid, flowing unevaporated refrigerantfrom said evaporator to a second place which serves as a place ofaccumulation for such liquid, the liquids in the first and second placesbeneath the surface levels thereof being in free liquid communication ina path which is always completely filled with liquid, arrestingabsorption liquid being circulated in its path of flow and retainingsuch arrested liquid in a third place. and redistributing the absorptionliquid in its path of flow, such redistribution of the absorption liquidincluding the step of substantially stopping the circulation ofabsorption liquid in its path of flow to promote renewal to said firstplace of absorption liquid retained in said third place.

2. In the art of refrigeration with the aid of a system in whichrefrigerant vapor is expelled from absorption liquid in a generator,refrigerant vapor is liquefied. liquid refrigerant evaporates in anevaporator, refrigerant vapor is absorbed into absorption liquid in anabsorber and absorption liquid is circulated in a path of flow throughand between the generator and absorber, the improvement which comprisesthe steps of maintaining a body of absorption liquid in a first place insaid path of flow for such liquid, flowing liquid refrigerant in thesystem to a second place which serves as a place of accumulation forsuch liquid, the liquids in the first and second places beneath thesurface levels thereof being in free liquid communication in a pathwhich is always completely filled with liquid, arresting absorptionliquid being circulated in its path of flow and retaining such arrestedliquid in a third place, and redistributing the absorption liquid in itspath of flow, such redistribution of the absorption liquid including thestep of modifying the normal circulation of absorption liquid in itspath of flow to promote removal of absorption liquid retained in saidthird place into said lastmentioned path of flow,

3. The improvement set forth in claim 2 in which refrigerant vapor isexpelled from absorption liquid in the generator by heating during on"periods of maximum heating alternating with off periods of reducedheating. the further step of retaining in said evaporator during theperiods of maximum heating unevaporated refrigerant which otherwisewould pass therefrom without producing useful refrigeration.

4. In the art of refrigeration with the aid of a system in which heat issupplied to a generator to expel refrigerant vapor from absorptionliquid therein, refrigerant vapor is liquefied, liquid refrigerantevaporates in an evaporator, refrigerant vapor is absorbed intoabsorption liquid in an absorber and absorption liquid is circulated ina path of flow through and between the generator and absorber by raisingliquid by vapor lift action due to said heat supply, the improvementwhich comprises the steps of maintaining a body of absorption liquid ina first place in said path of flow for such liquid, flowing liquidrefrigerant in the system to a second place which serves as a place ofaccumulation for such liquid, the liquids in the first and second placesbeneath the surface levels thereof being in free liquid communication ina path which is always completely filled with liquid, arrestingabsorption liquid being circulated in its path of flow and retainingsuch arrested liquid in a third place, and transferring absorptionliquid to said first place from other regions in its path of flow, suchtransfer of absorption liquid including the step of reducing the rate atwhich heat is supplied to effect raising of absorption liquid by vaporlift action to substantially terminate the circulation of absorptionliquid in its path of flow so as to promote transfer to said first placeof absorption liquid retained in said third place.

5. In the art of refrigeration with the aid of a system in whichrefrigerant vapor is expelled from solution in a generator, refrigerantvapor is liquefied, liquid refrigerant evaporates in an evaporator,refrigerant vapor is absorbed into absorption liquid in an absorber andabsorption liquid is normally circulated in a path of flow through andbetween the generator and absorber, the improvement which comprises thesteps of maintaining a body of absorption liquid in a first place insaid path of flow for such liquid, flowing unevaporated liquidrefrigerant from said evaporator to a second place which serves as aplace of accumulation for such liquid, the liquids in the first andsecond places beneath the surface levels thereof being in free liquidcommunication in a path which is always completely filled with liquid,arresting absorption liquid being circulated in its path of flow whichtherwise flows to said first place and retaining such arrested liquid ina third place, and transferring absorption liquid to said first placefrom other regions in its path of flow responsive to cessation of normalcirculation of such liquid in its path of flow, such transfer ofabsorption liquid including the step of promoting removal to said firstplace of absorption liquid retained in said third place.

6. In the art of refrigeration with the aid of a system in whichrefrigerant vapor is expelled from absorption liquid in a generator,refrigerant vapor is liquefied, liquid refrigerant evaporates in theevaporator, refrigerant vapor is absorbed into absorption liquid in theabsorber and absorption liquid is normally circulated in a path of flowthrough and between the generator and absorber, the improvement whichcomprises the steps of providing bodies of absorption liquid at firstand second places which are in free liquid communication with oneanother below the surface levels thereof in a path which is alwayscompletely filled with liquid, maintaining only the liquid body in saidfirst place in an active portion of said path of flow for absorptionliquid, the liquid body in said second place being in intimate physicalcontact with absorption liquid in the active portion of its path offi-ow only at said free liquid communication and during normalcirculation of absorption liquid essentially forming a stagnant liquidbody, flowing liquid refrigerant in the system to said second placewhich serves as a region in which such liquid is accumulated, arrestingabsorption liquid being circulated in its path of flow and retainingsuch arrested liquid in a third place, redistributing the absorptionliquid in the system to transfer such liquid to the first place, suchredistribution of absorption liquid including the step of effecting flowof such retained liquid from said third place in said path of flow forabsorption liquid by modifying the normal circulation of absorptionliquid in such path of flow, mixing accumulated liquid refrigerant andabsorption liquid by flowing absorption liquid from the first place tothe second place through said free liquid communication responsive totransfer of absorption liquid to said first place, and flowing saidmixture of liquid refrigerant and absorption liquid in said path of flowto said generator.

7. An absorption refrigeration system comprising circuits for normalcirculation of refrigerant and absorption liquid, the circuit forcirculation of absorption liquid including a generator and an absorberhaving a first vessel associated therewith for holding a body of suchliquid, a second vessel for holding a body of absorption liquid, thesurface level of liquid in said second vessel always rising and fallingresponsive to rise and fall, respectively, of the surface level of theliquid in said first vessel by passage means which connects said firstand second vessels and is completely filled with liquid under alloperating conditions of the system, the system including connections forconducting liquid refrigerant to said second vessel for accumulationtherein, means including said passage means for mixing such accumulatedrefrigerant with absorption liquid responsive to redistribution ofabsorption liquid in its circuit, structure for arresting and retainingabsorption liquid being circulated in its circuit and subsequentlyeffecting flow of such arrested and retained liquid in said absorptionliquid circuit to promote said redistribution of liquid therein, saidstructure being connected in said absorption liquid circuit along withsaid absorber, and said structure being disposed between said generatorand said first vessel in the path of flow of absorption liquid in itscircuit from the former to the latter.

8. An absorption refrigeration system as set forth in claim 7 in whichsaid structure for arresting and retaining absorption liquid beingcirculated in its circuit includes a vessel, and means for overflowingliquid from the surface level of the body of such arrested and retainedliquid during normal circulation of the absorption liquid.

9. An absorption refrigeration system as set forth in claim 8 is whichsaid structure for effecting flow of such arrested and retained liquidin said absorption liquid circuit includes provisions for effecting suchfiow responsive to change in an operating condition in the system.

10. An absorption refrigeration system as set forth in claim 9 in whichsaid structure for effecting flow of such arrested and retained liquidin said absorption liquid circuit includes provisions for effecting suchflow responsive to a reduction in the rate of flow of absorption liquidin its circuit.

11. An absorption refrigeration system as set forth in claim 10 in whichsaid provisions for effecting fiow of arrested and retained absorptionliquid for flow in said absorption liquid circuit includes a capillarylift.

12. An absorption refrigeration system as set forth in claim 11 in whichsaid capillary lift is capable of effecting flow of arrested andretained absorption liquid in said absorption liquid circuit at a ratewhich is less than that at which absorption liquid is normallycirculated in its circuit,

13. An absorption refrigeration system comprising circuits forcirculation of refrigerant, inert gas and absorption liquid, said inertgas circuit including an evaporator, said refrigerant circuit includingconduit means for conducting liquid refrigerant to said evaporator forgravity flow therethrough, said absorption liquid circuit including agenerator and an absorber having a first vessel associated therewith forholding a body of such liquid, a second vessel for holding a body ofabsorption liquid, the surface level of liquid in said second vesseialways rising and falling responsive to rise and fall, respectively, ofthe surface level of the liquid in said first vessel by passage meanswhich connects said first and second vessels and is completely filledwith liquid under all operating conditions of the system, the systemincluding connections for conducting liquid refrigerant to said secondvessel for accumulation therein, means including said passage means formixing such accumulated refrigerant with absorption liquid responsive toredistribution of absorption liquid in its circuit, structure forarresting and retaining absorption liquid normally being circulated inits circuit and subsequently effecting flow of such arrested andretained liquid in said absorption liquid circuit to promote saidredistribution of liquid therein, said structure being connected in saidabsorption liquid circuit along with said absorber, said structure beingdisposed between said generator and said first vessel in the path offlow of absorption liquid in its circuit from the former to the latter,and means for retaining liquid refrigerant in said evaporator.

14. An absorption refrigeration system as set forth in claim 13 in whichinert gas flows in counterfiow to refrigerant in at least that part ofsaid evaporator in which liquid refrigerant is retained therein.

15. An absorption refrigeration system having circuits for circulationof refrigerant and absorption liquid, the circuit for circulation ofabsorption liquid comprising a vapor expulsion unit including a pump forraising liquid by vapor lift action and an absorber including a firstvessel for holding a body of absorption liquid, a second vessel forholding a body of absorption liquid, the surface level of liquid in saidsecond vessel always rising and falling responsive to rise and fall,respectively, of the surface level of the liquid in said first vessel bypassage means which connects said first and second vessels and iscompletely filled with liquid under all operating Conditions of thesystem, the system including connections for conducting liquidrefrigerant to said second vessel for accumulation therein, and meansfor mixing such accumulated refrigerant with absorption liquidresponsive to transfer of such liquid to said first vessel from otherparts of said absorption liquid circuit, said other parts includingstructure connected in series with said absorber for arresting andretaining absorption liquid being circulated in its circuit when saidpump is rendered active to raise liquid by vapor lift action and forsubsequently effecting flow of such arrested and retained absorptionliquid to said first vessel when said pump is rendered inactive to raiseliquid by vapor lift action.

16. An absorption refrigeration system as set forth in claim 15 in whichsaid circuit for absorption liquid includes provisions for flowing themixture of liquid re frigerant and absorption liquid to said vaporexpulsion unit when said pump is rendered active to raise liquid byvapor lift action.

17. An absorption refrigeration system as set forth in claim 16 in whichsaid absorber includes a coil and said structure for arresting andretaining absorption liquid being circulated in its circuit foreffecting flow of such arrested and retained liquid to said first vesselis interposed between said coil and said first vessel.

18. An absorption refrigeration system as set forth in claim 17 in whichsaid structure comprises a storage vessel connected to receiveabsorption liquid from said coil and an overflow connectioncommunicating with said first vessel, and means including a wick toeffect flow of arrested and retained liquid from said storage vessel tosaid first vessel when said pump is rendered inactive to raise liquid byvapor lift action.

References Cited in the file of this patent UNITED STATES PATENTS1,924,770 Backstrom Aug. 29, 1933 2,210,609 Ullstrand Aug. 6, 19402,246,665 Bufiington June 24, 1941 2,465,904 McNeely Mar. 29, 19492,501,606 Kogel Mar. 21, 1950 2,583,722 Berestnetf Jan. 29, 1952

